Referring to FIG. 1, an articulated joint with a conventional lock device includes an outer casing pair 10, an inner casing pair 20, a lock block set 30, a spring 400, a trigger 50, a slidable element 70, a casing secure rivet 80 and a trigger locating rivet 90. The outer casing pair 10 is composed of two opposite outer casing shells 11, 12 and each of the outer casing shells 11, 12 has a circular upper section and an elongated lower section with a guide slot 13 at the intersection of the circular section and the elongated section and being disposed along radial direction of the circular section. A trigger locating hole 16 beside the sliding slot 13 near a lateral side of the respective outer casing shell 11, 12 for rotationally locating the trigger 50 with the trigger locating rivet 90. A secure hole 19 is provided at the bottom area of the lower section of the two outer casing shells 11, 12 for being fixedly attached to one of the rails on a ladder. Besides, the outer casing shell 12 has a spring seat 14 and the spring seat 14 is disposed below the guide slot 13 at the outer casing shell 12 with a pinhole 141 for locating the lock block set 300. The lock block set 300 includes a lock block 310, a fixing plate 350 and a locating pin 320. The lock block 310 has a blind hole at an elongated side thereof and the fixing plate 350 basically is a short U shaped sheet with a central through hole and two opposite extending outward lateral sides. The lock block 310 sits on the fixing plate 350 with the side having the blind hole aligning with the through hole of the fixing plate 350 and an end of the locating pin 320 enters the blind hole via the through hole and the pinhole 141 being passed through by another end of the locating pin 320. The spring 400 surrounds the locating pin 320 with an end of the spring 400 touching the spring seat 14 and another end of the spring 400 touching the lower side of the lock block 31. The inner casing pair 20 is composed of two opposite inner casing shells 21, 22. Each of the inner casing shells 21, 22 has an upper circular section and an elongated lower section too and provides three locating recesses 231, 232, 233 for catching the lock block 310. Further, each of the inner casing shells 21, 22 has three arc slots 24 for receiving three short pins 60 attached to the slidable element 70 and allowing the short pins 60 with the slidable element 70 moving along the arc slots 24. Further, the inner casing shell 22 has a locating tongue 25 at the lower part of the circular section thereof for locating an end of an extension spring 71, which has the other end thereof being attached to an end of the slidable element 70. The inner casing shells 21, 22 provide fixing holes 29 for being fixedly attached to a rail of another ladder part of the foldable ladder with rivets. In addition, the trigger 50 has the upper part contacting the lock block 310 and the top edge thereof pressing against the slidable element 70 at the lowermost short pins. The inner casing pair 20 and the outer casing pair 10 are rotationally joined together. Once the outer casing shells 11, 12 are joined to each other, a space is constituted between the upper circular sections of the outer casing shells 11, 12 for positioning the inner casing pair 20. While the trigger 50 is pressed to move the lock block 310 out of one of the locating recesses 231, 232, 233 and an angle between the outer casing pair 10 and the inner casing pair 20 can be adjusted till the lock block 31 enter another one of the locating recesses 231, 232, 233.
As the foregoing, the lock device, which is composed of the lock block 310, the fixing plate 350, the locating pin 320 and the spring 400, is detachable such that it is easy for the parts of the lock device become loosening apart from each other during the foldable ladder being in use. As a result, it is very possible to happen unexpected accident.